A Proof of Principle for the Phase-Dependent Electrocatalytic Activity of NiTi Shape Memory Alloys for Oxygen Evolution Reaction

Abstract

Nickel-titanium (NiTi) shape memory alloys are intermetallic compounds which can exhibit a reversible martensitic phase transformation. While extensively studied for biomedical and actuator applications, their potential as electrocatalysts for the oxygen evolution reaction (OER) remains virtually unexplored. Here, we systematically investigate how phase structure influences OER activity in NiTi alloys by comparing martensite Ni₅₀Ti₅₀ (B19' monoclinic) and austenite Ni₅₁.₂Ti₄₈.₈ (B2 cubic). Despite differing by only 1.2 at.% Ni, the investigated specimens exhibit markedly different electrocatalytic behavior. In 1 M KOH containing 15 ppb Fe, the martensitic one requires 40 mV lower overpotential (450 mV vs. 490 mV at 10 mA cm⁻²) and maintains stable operation at 1.56 V vs. RHE over 12 hours. This improved activity correlates with characteristic phase-dependent properties: enhanced electrical conductivity, finer surface texture, and a markedly increased hydrophilicity of martensite (contact angle 21° vs. 71°). The martensitic phase also shows a 10% larger electrochemically active surface area. Under elevated Fe levels (150 ppb), the martensite phase undergoes stronger surface restructuring and achieves a 370 mV lower overpotential, indicating superior Fe incorporation compared to austenite. Together, these findings demonstrate that the OER performance in NiTi alloys is systematically tunable via their microstructural states and establish phase engineering of intermetallic shape memory alloys as a promising strategy for rationally designing next-generation electrocatalysts for water splitting.